280 REPORTS ON THE STATE OF SCIENCE. 



picrate of soda into which hydrocyanic acid has diffused or has been 

 distilled (fig. 5). 



The colour of the compound produced by the reaction (sodium is 

 iso-purpurate) is remarkably stable. It is not changed by prolonged 

 exposure to direct sunlight, nor by boiling. Its intensity is such that 

 a convenient unit is afforded by one milligramme HON per litre of 

 dilute picrate (picrate acid 0*1; sodium carbonate 1; water 100). 



For practical use it is convenient to prepare two scales: — 



T 1 to T 10 containing 1 to 10 milligrammes HON per litre 

 T 01 to T 1 „ 0-1 to 1 



The coarser of these two scales is intended for use in ordinary 

 2-ounce bottles with 50 c.c. of liquid ; the finer for use in flat-bottomed 

 tubes of the Nessler type with 20 c.c. of liquid. 



In either case the actual estimation consists in the determination 

 of a colour number, T, which indicates millionths of a gramme HON 

 per 1 c.c, and gives therefore by simple multiplication by the number 

 of c.c. the absolute amount of HON present in any given volume — 

 e.g., a tint 



T 1 in 100 c.c. = 0-000100 grm. HON 

 T 3 in 50 c.o. = 0000150 

 T 0-5 in 20 c.c. = 0-000010 



There is no danger of confusing HON with either sugar or creatinin, 

 since neither of these substances are volatile. In the case of animal 

 tissues, acetone, if present, produces only a very slight discoloration, 

 and is readily recognised by the iodoform test. 



Illustrative Experiments. 



The application of the method as regards laurel leaves will be most 

 clearly appreciated by inspection of figs. 4 and 5. As regards animal 

 tissues, it will be sufficient to quote four experiments from among many 

 others. 



Exp. 12.— Oat, 2 kilos. Death by injection of 0"005 grm. KCN 

 ( = '002 grm. ON). Distillates of 10 grm. into 10 c.c. picrate. 



Exp. 13 (control). — Oat, 2 - 5 kilos. Death by chloroform at 5 per 

 cent. Distillates as in Exp. 12 of blood, brain, heart, and muscle gave 

 no discoloration, i.e. no sign of HON. 



Observation 24. — Man, aged sixty, found dead in bed on the morning 

 of June 21. Distillates taken on June 23 of 10 grm. of tissue into 

 10 c.c. of picrate to a volume of 20 c.c. 



Distillate 1. Blood 

 „ 2. Brain 

 „ 3. Heart 

 ,, 4. Muscle 

 „ 5. Viscera 



(and contents) 



T 2 . . .40 (10-° grm. HCN) 



T 1 . . .20 



T2 . . .40 



TO-5 . .10 



T20 . . 400 



